Structure and Leukemogenic Activity of a Murine Leukemia Virus

Purified Friend viruses obtained from chronically infected tissue cultures were studied under the electron microscope in an effort to correlate the fine structure of the particles to their leukemogenic activity under varied experimental conditions, i.e., temperature treatments and exposure to Tween 80, amyl acetate, or ether. It was observed that an intact viral envelope was a prerequisite to leukemogenic activity as tested by intraperitoneal inoculation of newborn mice. It was also noted that the percentage of C particles was not increased after heating for 1 hr at 45 C (treatment which, however, completely inactivated the viruses). Digestion with ribonuclease indicated the presence of ribonucleic acid within the nucleoids of "enveloped A particles," which shows that these are not immature particles. The significance of the simultaneous presence of "enveloped A" and C particles is discussed.     

Pathogenicity of Chlamydia psittaci after serial passage in chicken embryos

The virulence in pregnant ewes of a single strain of $\text{Chlamydia psittaci}$ was tested after the following treatments: (a) 110 serial passages in chicken embryos (CE) incubated at 37 C, and (b) 7 CE passages at 37 C followed by 10 CE passages at 40 C. Neither treatment caused significant reduction in abortions (P > 0.3) nor incidence of ewes shedding chlamydia in placentas or vaginal discharges (P > 0.5) compared to ewes inoculated with the original virulent strain.     

The effects of serial passage of a nucleopolyhedrosis virus through an alternate host system

The multiple-embedded velvetbean caterpillar nucleopolyhedrosis virus (VBC-NPV) ofAnticarsia gemmatalis Hübner was shown to be infectious of a variety of noctuid hosts. The mortality data demonstrated the importance of defining the dosage used in host range analysis. Serial passage of the VBC-NPV through the soybean looper,Pseudoplusia includens, was done to select for host range variants of this NPV. After several passages of the VBC-NPV through this insect the virulence of the progeny virus remained unchanged indicating heterogeneity in the host and not the virus population. However, between the 3rd and 5th serial passage throughPseudoplusia a latent NPV identical to a single-embedded NPV previously associated fromA. gemmatalis was activated. The biological and biochemical characteristics of this isolate demonstrated it to be distinct from the original VBC-NPV. A single passage of this activated virus throughA. gemmatalis resulted in the production of viral progeny having characteristics of the original VBC-NPV. Serial passage of this virus preparation throughP. includens resulted in virus progeny having biological properties associated with both the original VBC-NPV and the activated NPV isolate.     

Loss of graft-versus-host reactivity of mouse lymphocytes during serial passage through irradiated allogeneic hosts

Lymphoid cells which are injected into heavily x-irradiated allogeneic mice proliferate in the recipient spleens and exhibit immunological reactivity against cells of recipient genotype. We have tested whether the immunological reactivity of such cells can be further increased by injections into irradiated secondary and tertiary hosts of the same genotype. Cellular immunity of the cells was measured in a graft-vs-host test which is based on the principle that lymphocytes can inhibit the proliferation of allogeneic bone marrow cells in the spleens of irradiated recipients.Cells obtained from lymph nodes or thymi exhibited an increased graft-vs-host reactivity after five days' residence in the spleens of irradiated allogeneic mice. Attempts to sensitize these cells further by injection into secondary and tertiary irradiated recipients of the same genotype resulted in a progressive loss of their graft-vs-host reactivity. Cell counts in the spleens indicated that the proliferative activity was highest for nonsensitized and lowest for sensitized cell populations, indicating that the decline in immunological activity may be due to a decreased proliferative activity of the cells as a result of the response to the specific antigens.     

Behavior of the Y and Peruvian strains of Trypanosoma cruzi in mice, after passage through various media

The behavior of two strains of Trypanosoma cruzi (Y and Peruvian strains) in experimental mouse infection, after being passed through different conditions of maintainance and cultivation was studied. The conditions were: Warren's acellular culture medium, cryopreservation in liquid Nitrogen, passage through the insect vector and direct blood passage from mice to mice. The parameters considered for comparative study were as follows: parasitemia, mortality rate, maximum survival time, morphology of parasites in peripheral blood, tissue tropism and histopathological lesions. Each experimental group consisted of two sub-groups according to the inocula: 10.000 or 50.000 trypomastigotes. The basic characteristics of the strains remained unchanged. These were macrophagotropism, predominance of slender forms of the parasite in early infection and 100 per cent mortality rate in the acute phase of the infection. However, decrease in the virulence was observed when the culture forms were used or when the infection with low inoculum was used (10.00 forms). Therefore the main biological characteristics of the strains tended to remain the same, regardless of the conditions used for maintainance and cultivation.     

Influence of serial passage on the infectivity and immunogenicity of Nematospiroides dubius in mice

Dobson C. and Owen M. E. 1977. Influence of serial passage on the infectivity and immunogenicity of Nematospiroides dubius in mice. International Journal for Parasitology7: 463–466. The infectivity of Nematospiroides dubius was increased for Quackenbush (Q) mice by ten serial passages through this host. At the same time C(In3)H mice became more refractory to infection with successive Q generations of the parasite. Both strains of mice rejected the most highly selected parasites more readily than parasites from the earlier generations. These responses were shown to be immunological in nature by infections in hypothymic Balb/c CBA nu/nu and nu/+ mice and to be dose dependent. The selection of N. dubius for increased infectivity in Q mice enhanced its immunogenicity in this and other mouse strains possibly because of increased genetic homogenicity in the selected populations. N. dubius selected for Q mice showed a degree of immunologieal adaptation to Q but not to C₃H mice.     

Strain selection during serial passage of Trichoplusia in nuclear polyhedrosis virus.

Two strains of a nuclear polyhedrosis virus (NPV) of Trichoplusia ni were isolated on the basis of plaque morphology. They are designated as MP (having greater than 30 polyhedra per nucleus) and FP (having fewer than 10 polyhedra per nucleus). Serial, undiluted passage of plaque, purified MP nonoccluded. Virus (NOV) in tissue culture led to the production of the FP phenotype detectable at passage 9. With continued serial, undiluted passage, FP became the predominant strain. Comparative growth curves showed that FP NOV are released faster than MP NOV. MP morphology was not observed after 14 serial, undiluted passages of plaque-purified FP. By the plaque neutralization assay, NOV from both strains of virus was neutralized by the homologus and heterologous antisera. The FP phenotype was observed when FP virus was grown in culture at 17, 22, and 27 C. Hence, the FP phenotype was not considered to be the result of temperature-inhibited crystallization of polyhedrin under standard tissue culture conditions. The NOV of both strains killed insects when injected directly into the hemocoele of T. ni larvae. Only MP inclusion bodies were virulent per os. The FP inclusion bodies fed to cabbage looper larvae did not kill, and no infectious agent could be detected in the hemolymph. Electron micrographs of MP polyhedra showed bundles of nucleocapsids of normal length within the polyhedra, whereas FP polyhedra contained heterogeneous, electron-dense material, which could account for their lack of pathogenicity.     

Propagation of fetal human RPE cells: preservation of original culture morphology after serial passage

The permissive effects of extracellular matrix (ECM) on in vitro growth and differentiation of fetal human retinal pigment epithelial (RPE) cells have been studied. Factors which enhanced the effect of ECM to support cell division were also examined, including growth factors, culture media, and serum requirement. Under the specific culture conditions we have defined, it is possible to propagate these RPE cells at low density (less than 20 cells/mm2) with excellent growth properties for greater than 72 doublings (fourteen passages) in serial culture. Later-passaged cells maintained the morphological appearance of early-passaged cultures. ECM produced by bovine corneal endothelial cells was by far the most predominant factor in promoting rapid cell proliferation and viability over repeated passaging. Basic fibroblast growth factor (bFGF) exerted a substantial effect on the rate of cell division at different serum concentrations on plastic dishes. In addition, this factor showed profound synergistic effect when RPE cells were maintained on ECM, both in the preservation of cell morphology and also in long term viability. Other growth factors, such as epidermal growth factor (EGF) and transforming growth factor-beta (TGF-B), were also tested, but EGF effects were less prominent than those observed with bFGF, and TGF-B had an inhibitory effect at high concentrations. The ability to obtain a relatively large number of human RPE cells in vitro which preserve the appearance of early passage cells may provide useful opportunities to study the physiological properties and pathological alterations involving this important cell type.     

Viability of dinoflagellate cysts after the passage through the copepod gut

Several dinoflagellate species form nonmotile, thick-walled resting cysts in their life cycle. Cysts can be ingested by planktonic and benthic organisms, but there is scarce information concerning their survival after the passage through the digestive apparatus of the grazers. We tested the germination capability of cysts produced by two neritic dinoflagellates, Scrippsiella trochoidea (F. Stein) A.R. Loeblich and Scrippsiella ramonii Montresor, after their ingestion by four copepod species. Experiments have been carried out with four species: Acartia clausi Giesbrecht, 1889; Centropages typicus Kröyer, 1849; Temora stylifera Dana, 1849; and Clausocalanus lividus Frost and Fleminger, 1968. Copepods were fed either with motile cells or cysts, and feeding and clearance rates were estimated for A. clausi, C. lividus and T. stylifera. Grazing rates on both dinoflagellates was much higher for vegetative cells than for cysts. Resting cysts were isolated from the faecal pellets and incubated to test their germination capability. S. trochoidea cysts eaten by C. typicus and T. stylifera showed a high germination rate, while cysts of the same species were not viable after the passage through the gut of A. clausi and C. lividus. In contrast, S. ramonii cysts were never able to germinate after being ingested by copepods. The observed variation in viability among the two cyst types and the different survival rates observed for S. trochoidea cysts might be related to differences in cyst morphology and to differences in the digestive process among the tested copepod species.     

Increased virus replication and virulence after serial passage of human immunodeficiency virus type 2 in baboons

Similar to human immunodeficiency virus type 1 (HIV-1) infection of humans, the natural history of HIV-2 infection in baboons (Papio cynocephalus) is a slow and chronic disease that generally takes several years before an AIDS-like condition develops. To shorten the amount of time to the development of disease, we performed five serial passages of HIV-2(UC2) in baboons by using blood and bone marrow samples during the acute phase of infection when viral loads were at high levels. After these serial passages, virus levels in plasma, peripheral blood mononuclear cells (PBMC) and lymphatic tissues in the acutely infected baboons were increased. Within 1 year of the HIV-2 infection, all of the inoculated baboons showed specific signs of AIDS-related disease progression within the lymphatic tissues, such as vascular proliferation and lymphoid depletion. The HIV-2(UC2) recovered after four serial passages showed increased kinetics of viral replication in baboon PBMC and cytopathicity. This study suggests that the HIV-2 isolate recovered after several serial passages in baboons will be useful in future studies of AIDS pathogenesis and vaccine development by using this animal model.